The present invention pertains to detection apparatus and more particularly, to apparatus for detecting, on a vital or fail-safe basis, the presence and position of individual wheel-axles of railroad cars, in a detection zone.
As background material for an understanding of the apparatus and technique of the present invention, reference may be made to the following patents: British Pat. No. 767,724; U.S. Pat. No. 3,697,455; U.S. Pat. No. 4,058,279 and U.S. Pat. 4,351,504; the last two mentioned patents being assigned to the assignee of the present invention. In accordance with the last-cited patent, there is described apparatus for sensing the presence of a car wheel by sensing a shunt current flowing through the car wheel-axle set. However, that system depends upon the presence of the car wheel in a detection zone or region to develop a suitable output voltage. In other words, in the event that a car wheel is not present, no substantial output signal is available to be sensed, an identical result to what certain failures in the system will produce.
The system of the present invention represents an improvement on the detection system of U.S. Pat. No. 4,351,504. In particular, instead of a standard track circuit wheel detector system, which is not capable of producing so called vital or fail-safe indications, the present improvement is concerned with enabling a vital, or fail-safe basis of operation. By vital or fail-safe operation is meant an operation which provides the most restrictive kind of output. For example, in the detection system under consideration, it is desired that in the event that there are open circuits or other failures present, a signal will be given that identifies such conditions, and represents such conditions as analogous to the presence of wheel-axles in the detection zone.
Accordingly, it is a primary object of the present invention to provide a vital, directional, wheel detection system that will permit detection of the presence and position of wheel-axles in a detection zone or section.
In fulfillment of the above-noted object, a primary feature of the present invention resides in a system for detecting the presence and position of railroad car wheel-axles in which a transmitter having a high frequency output is connected to a pair of rails which, together with suitable shorting means, constitute a path for the flow of high frequency current from said transmitter. A sensing means, including a pick-up coil, is provided to give a relatively sharp or abrupt indication when a wheel or wheel-axle combination is present in a detection zone. The sensing means also includes a biasing arrangement which provides a steady flow of bias current. When the "wheel-axle presence and position" output signal is generated, it acts to counter or oppose the bias current normally present. Thus an abrupt, negative-going output signal is detected responsive to the presence of the wheel-axles. However, if there are open circuit conditions present, a restricted output will be provided i.e. an output comparable to the presence of wheel-axles in the detection zone.
Another feature of the present invention resides in the particular arrangement for producing bias current. This can take the form of a coil means for feeding a small amount of bias current from the feed loop to a pick-up coil, or alternatively, it can take the form of a self-biasing arrangement whereby the pick-up coil itself develops a bias current by sensing the feed current present in one of the rails or the feed wire of the system. Other alternative schemes or arrangements and modifications thereof will be described.
Another feature relates to the way in which the output signal responsive to the presence of a wheel-axle is caused to develop. In one embodiment, this output signal is developed in response to all of the components of current flowing up through the wheel axle; that is, the vertical component of current through the radius of the wheel and the horizontal component through the axle itself. In another embodiment, which features a different arrangement for feeding the high frequency current to the rails, the pickup coil of the sensing means not only has currents induced in it from the rail, but is further effected by the current through the radius of the wheel only. However, it is not affected by current through the axle, nor current flowing in the feed wire or the shunt strap. In this embodiment the pick-up coil is located somewhere on a 45.degree. angle plane bisecting the angle between the rail and the vertical wheel radius, assuming a location near to the center of the detecti zone.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawing, wherein like parts have been given like numbers.